Switch Mode Power Supply (SMPS) is widely used for converting an input voltage into an output voltage and supplying a load, due to its many advantages such as high efficiency, high current carrying ability and so on. The output voltage is usually regulated by controlling a duty cycle of a power switch where the duty cycle is the ratio of the on time in a cycle period. SMPS comprises many topologies such as boost converter, buck converter, flyback converter, etc.
FIG. 1 illustrates a prior art boost converter for converting an input voltage Vin at an input port IN into an output voltage Vout at an output port OUT, wherein the output voltage Vout is higher than the input voltage Vin. The output voltage Vout is regulated under the switching action of a power switch Q which is coupled between a switching node SW and a reference ground GND. Boost converter further comprises an inductor L1 coupled between input port IN and switching node SW, a rectifier D1 coupled between switching node SW and output port OUT, and an output capacitor Gout coupled between output port OUT and reference ground GND. However, when power switch Q is in ON state and if switching node SW is electrically shorted to input voltage Vin, current flowing through power switch Q would increase dramatically and power switch Q would be damaged. Thus, a short protection circuit is required to protect power switch Q from being damaged when switching node SW is shorted to a high voltage rail such as input port IN.
Conventional short protection circuit normally uses a current amplifier for sensing the current flowing through power switch Q and a current comparator for comparing the current signal with a maximum current reference. When the current signal rises above the maximum current reference, power switch Q is turned off. However, the current comparator is required to have high accuracy which would have a long response delay. Due to the delay of the current sense amplifier, the delay of the current comparator and the other delays, the current flowing through power switch Q at the time when power switch Q is turned off is much higher than the maximum current reference. And power switch Q would be damaged.
Accordingly, a short protection circuit is required to at least address one or some of the above deficiencies.